1. Field of the Invention
The present invention relates generally to liquid processing apparatuses, liquid processing methods, and liquid condition detection apparatuses, and particularly to liquid processing apparatuses and methods for example supplying photoresist or a similar prescribed processing liquid to a substrate's surface to process it as prescribed, and liquid condition detection apparatuses detecting whether the liquid has fluctuation.
2. Description of the Background Art
Conventionally a semiconductor fabrication process includes a photoresist step, at which photoresist serving as a prescribed processing liquid is applied on a surface of a substrate such as a semiconductor wafer (hereinafter simply referred to as a “wafer”), and then exposed to light and then developed with a developing agent to form a mask pattern on the surface. Generally, such a process is performed in a system having an application and development apparatus applying and developing photoresist, with an exposure apparatus connected to.
One technique employed to apply on the wafer's surface a liquid to be applied corresponding to a processing liquid, is spin coating. A liquid processing unit applied to this technique will now be simply described with reference to FIG. 14. Initially, a wafer W is held on a spin chuck 101 horizontally and a nozzle 110 jetting a liquid to be applied is set at a position opposite to a surface of wave W and jets the liquid fed via a path 111 from a source 112, such as a tank, supplying the liquid to supply the liquid on the wafer W surface at a center as wafer W is rotated around a vertical axis. The liquid is thus centrifugally spread across the wafer W surface to form a film of the liquid.
If a film of a liquid to be applied is formed on the wafer W surface to have a desired thickness, a set value in concentration of a component contained in the liquid to be applied that forms the film or the like serves as an important processing parameter. Conventionally, liquids having different levels of concentration corresponding to different thicknesses are prepared and a plurality of application systems are incorporated into an apparatus to allow each liquid having a different concentration to be independently supplied to wafer W, and in accordance with a target value in thickness as desired an appropriate system is selected to supply wafer W with a liquid of an optimum concentration. The existence of the plurality of application systems in the apparatus, however, complicates the apparatus's structure.
To address this disadvantage, for example as shown in FIG. 15, upstream of path 111 a branch is introduced and connected through paths respectively to a tank 113 storing a liquid concentrate of the liquid to be applied and a tank 114 storing a solvent corresponding to a concentration adjusting agent such as thinner. The liquid concentrate feeding path and the solvent feeding path meet at a mixture block 115a and downstream thereof a mixture means such as a line mixer 115 is arranged to change a ratio applied to mix the liquid concentrate and the solvent to prepare a liquid to be applied having an optimal concentration corresponding to a target value in thickness (see Japanese Patent Laying-Open No. 10-272407, for example). This approach is advantageous in that simply preparing a liquid concentrate and a solvent suffices to prepare liquids to be applied having different levels of concentration and the apparatus can dispense with the plurality of systems supplying liquids.
The above approach, however, has the following disadvantage: although it depends on how long path 111 is, a short but substantial period of time is required after a mixture ratio is changed and before a liquid present in a path extending from line mixer 115 to the nozzle 110 mouth is replaced and a liquid to be applied having an intended concentration is jet out the mouth. If a liquid which does not have the intended concentration should erroneously be applied on wafer W, a film of the liquid uneven in thickness in-plane results. This can contribute to an increased number of wasteful wafer W that cannot be used to manufacture products, and hence increased cost. As such, whether a liquid to be applied jetted out nozzle 110 has attained an intended concentration, i.e., whether an optimal liquid can be applied on wafer W, needs to be determined.
To detect a ratio between a liquid to be applied and a solvent mixed together by line mixer 115, a technique is employed, as follows: downstream of line mixer 115, path 111 is branched and a viscometer is arranged to measure a received liquid in viscosity and the mixture ratio is controlled so that the measured viscosity's value attains set values in viscosity corresponding to different target values in thickness (see Japanese Patent Laying-Open No. 2000-009655, for example). This approach is disadvantageous, however, in that if a viscometer in accordance with the JIS standard is used, its mechanism only allows a sampled liquid to be measured in a substantially still condition, and the viscometer cannot be incorporated in-line.